A thermal extrapolation method for the effective temperatures and internal energies of activated ions

Meot‐Ner, Michael; Somogyi, Árpád

doi:10.1016/j.ijms.2007.04.007

Cited by 15 publications

(1 citation statement)

References 62 publications

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“…Experimentally, the decrease of the stepwise water addition enthalpies to smaller negative values of −8 to −10 kcal mol –1 , compared with −10.5 kcal mol –1 for the bulk condensation enthalpy, has been observed in many series of small hydrated ion clusters of 6–8 water molecules . However, in the particular case of the hydrated hydronium H 3 O + /(H 2 O) N w series, an experimental study found Δ H N w –1, N w of a nearly constant value, 10–11 kcal mol –1 , for N w = 14–28, and these bulk-like values are not likely to change up to bulk solution.…”

Section: Results and Discussionmentioning

confidence: 99%

Simulated Solvation of Organic Ions: Protonated Methylamines in Water Nanodroplets. Convergence toward Bulk Properties and the Absolute Proton Solvation Enthalpy

2014

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We applied an alternative, purely theoretical route to estimate thermodynamical properties of organic ions in bulk solution. The method performs a large ensemble of simulations of ions solvated in water nanodroplets of different sizes, using a polarizable molecular dynamics approach. We consider protonated ammonia and methylamines, and K(+) for comparison, solvated in droplets of 50-1000 water molecules. The parameters of the model are assigned from high level quantum computations of small clusters. All the bulk phase results extrapolated from droplet simulations match, and confirm independently, the relative and absolute experiment-based ion solvation energies. Without using experiment-based parameters or assumptions, the results confirm independently the solvation enthalpy of the proton, as -270.3 ± 1.1 kcal mol(-1). The calculated relative solvation enthalpies of these ions are constant from small water clusters, where only the ionic headgroups are solvated, up to bulk solution. This agrees with experimental thermochemistry, that the relative solvation energies of alkylammonium ions by only four H2O molecules reproduce the relative bulk solvation energies, although the small clusters lack major bulk solvation factors. The droplet results also show a slow convergence of ion solvation properties toward their bulk limit, and predict that the stepwise solvation enthalpies of ion/water droplets are very close to those of pure neutral water droplets already after 50 water molecules. Both the ionic and neutral clusters approach the bulk condensation energy very gradually up to 10,000 water molecules, consistent with the macroscopic liquid drop model for pure water droplets. Compared to standard computational methods based on infinite periodic systems, our protocol represents a new purely theoretical approach to investigate the solvation properties of ions. It is applicable to the solvation of organic ions, which are pivotal in environmental, industrial, and biophysical chemistry but have been little investigated theoretically up to the present.

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Section: Results and Discussionmentioning

confidence: 99%

Simulated Solvation of Organic Ions: Protonated Methylamines in Water Nanodroplets. Convergence toward Bulk Properties and the Absolute Proton Solvation Enthalpy

2014

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Current literature in mass spectrometry

2008

J. Mass Spectrom.

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In order to keep subscribers up‐to‐date with the latest developments in their field, John Wiley & Sons are providing a current awareness service in each issue of the journal. The bibliography contains newly published material in the field of mass spectrometry. Each bibliography is divided into 11 sections: 1 Reviews; 2 Instrumental Techniques & Methods; 3 Gas Phase Ion Chemistry; 4 Biology/Biochemistry: Amino Acids, Peptides & Proteins; Carbohydrates; Lipids; Nucleic Acids; 5 Pharmacology/Toxicology; 6 Natural Products; 7 Analysis of Organic Compounds; 8 Analysis of Inorganics/Organometallics; 9 Surface Analysis; 10 Environmental Analysis; 11 Elemental Analysis. Within each section, articles are listed in alphabetical order with respect to author (4 Weeks journals ‐ Search completed at 27th. Feb. 2008)

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A determination of the effective temperatures for the dissociation of the proton bound dimer of dimethyl methylphosphonate in a planar differential mobility spectrometer

Eiceman

Stone

2010

Int. J. Ion Mobil. Spec.

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The dissociation of the proton bound dimer of dimethyl methylphosphonate to the protonated and neutral molecule has been studied in a planar differential mobility spectrometer. The internal energy of the ions is the sum of the thermal component and the electric field component and results in an effective temperature, T eff , that is significantly greater than that of the ambient atmosphere temperature, T. The measured rate constant for dissociation, which rises exponentially with field strength, together with activation energy and pre-exponential factor previously determined under thermal conditions, allow the calculation of T eff as a function of electric field strength. T eff is a linear function of electric field intensity at constant T over the range of T from 60°C to 140°C. The efficiency of the available collision energy in causing dissociation decreases with increasing T, from 52% at 60°C to 40% at 140°C.

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A thermal extrapolation method for the effective temperatures and internal energies of activated ions

Cited by 15 publications

References 62 publications

Simulated Solvation of Organic Ions: Protonated Methylamines in Water Nanodroplets. Convergence toward Bulk Properties and the Absolute Proton Solvation Enthalpy

Simulated Solvation of Organic Ions: Protonated Methylamines in Water Nanodroplets. Convergence toward Bulk Properties and the Absolute Proton Solvation Enthalpy

Current literature in mass spectrometry

A determination of the effective temperatures for the dissociation of the proton bound dimer of dimethyl methylphosphonate in a planar differential mobility spectrometer

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